LISTEN(3P)                                          POSIX Programmer's Manual                                         LISTEN(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       listen - listen for socket connections and limit the queue of incoming connections

SYNOPSIS
       #include <sys/socket.h>

       int listen(int socket, int backlog);


DESCRIPTION
       The listen() function shall mark a connection-mode socket, specified by the socket argument, as accepting connections.

       The backlog argument provides a hint to the implementation which the implementation shall use to limit the number of out-
       standing connections in the socket's listen queue. Implementations may impose a limit on backlog and silently reduce  the
       specified  value. Normally, a larger backlog argument value shall result in a larger or equal length of the listen queue.
       Implementations shall support values of backlog up to SOMAXCONN, defined in <sys/socket.h>.

       The implementation may include incomplete connections in its listen queue. The limits on the number of incomplete connec-
       tions and completed connections queued may be different.

       The  implementation  may  have an upper limit on the length of the listen queue-either global or per accepting socket. If
       backlog exceeds this limit, the length of the listen queue is set to the limit.

       If listen() is called with a backlog argument value that is less than 0, the function behaves as if it  had  been  called
       with a backlog argument value of 0.

       A  backlog  argument of 0 may allow the socket to accept connections, in which case the length of the listen queue may be
       set to an implementation-defined minimum value.

       The socket in use may require the process to have appropriate privileges to use the listen() function.

RETURN VALUE
       Upon successful completions, listen() shall return 0; otherwise, -1 shall be returned  and  errno  set  to  indicate  the
       error.

ERRORS
       The listen() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EDESTADDRREQ

              The socket is not bound to a local address, and the protocol does not support listening on an unbound socket.

       EINVAL The socket is already connected.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EOPNOTSUPP
              The socket protocol does not support listen().


       The listen() function may fail if:

       EACCES The calling process does not have the appropriate privileges.

       EINVAL The socket has been shut down.

       ENOBUFS
              Insufficient resources are available in the system to complete the call.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       accept(), connect(), socket(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    LISTEN(3P)